Email is so old school. These days, small businesses that are getting the most out of their smartphones and iPads are all about the apps: add-on programs that can help them do everything from process credit cards to sketch skyscrapers.

Of the small businesses surveyed in a March poll by AT&T Inc., 72% said they were using mobile apps. Thirty-eight percent reported they would struggle to survive without them.

Here’s a look at how Chicago entrepreneurs are using apps to transform their businesses, plus recommendations on which new ones might fit in their collections.

Lisa’s Clarinet Shop in Lombard takes in more than $1 million annually, but it’s only a 15-hour-per-week job for owner Lisa Canning. Ms. Canning, 47, sees clients by appointment and doesn’t keep regular hours, so she hasn’t invested in a traditional credit card terminal for the shop. That’s led to some awkward sales: She would write down each customer’s credit card information, take it home, process the card at her terminal there and then email a receipt to the customer.

That changed with the app Square. Using a small, free credit card reader provided by San Francisco-based Square Inc., Lisa’s Clarinet Shop can process credit card transactions for a 2.75% fee; there are no monthly fees or setup costs.

“I was embarrassed by my old-fashioned way of taking credit cards,” Ms. Canning says. “I built a great reputation online, but when people would come in and I (couldn’t charge them there), it felt unprofessional. Now I’m consistent. This was a no-brainer, and it also produces a really positive reaction from my customers that reflects well on me.”

Square, founded in 2009 by Twitter creator Jack Dorsey, is growing quickly. Tech industry publication TechCrunch reported that the company is valued at $1 billion in its current fundraising efforts.

WHY IT WORKS: “There is a good reason why Square is already attracting a $1-billion valuation by investors,” says Brad Spirrison, managing editor of Appolicious Inc. “Business owners like it for its simplicity and the fact that it doesn’t require monthly fees, a merchant account or contract.”

SOMETHING ELSE TO TRY: “If your business finances are already run through another service, the Intuit GoPayment credit card terminal and the Authorize.Net credit card terminal are also good apps to turn your phone or tablet into a mobile cash register,” Mr. Spirrison says.

Photographer David Ettinger, right, uses an array of apps: Simplenote and Evernote for note-taking, Toodledo to make to-do lists, TripCubby to track mileage and Google Earth to scout locations for shoots.

In David Ettinger‘s gear case, you’ll find the collection of lenses, lights and camera bodies that you’d expect from a professional photographer. It’s nothing, however, compared to the staggering array of mobile apps he uses to run his Chicago business, David Ettinger Photography.

First, there are two note-taking apps, Simplenote and Evernote. Both apps are free; Evernote is more full-featured (you can include voice memos, photos and notes with formatted text), while Mr. Ettinger finds Simplenote to be faster. Lately, he’s been using Simplenote to collect all of his notes about a particular job inside unformatted text files.

“When I’m mobile, I want to be as fast as possible, even if it comes at the expense of features,” Mr. Ettinger says. “I hate being that guy standing there at the end of the aisle at the store, waiting for something to load.”

Then he breaks his notes down into specific tasks and enters them into Toodledo, the to-do list app he uses both to track his agenda and for record-keeping. It’s a $1.99 app that utilizes Seattle-based Toodledo.com’s cloud-storage system so that to-do items will sync across multiple devices. There’s a free version of the service, but Mr. Ettinger subscribes to a $14.95-per-year plan that allows him to store two years’ worth of completed tasks online.

Then there are the specialized apps: TripCubby, to track mileage; Analytics, for checking his website and blog traffic, and Google Earth, to scout outdoor locations.

“I can work wherever I need to work,” he says. “A big part of my business is being accessible to my clients when they need me.”

WHY IT WORKS: “Simplenote is basically a premium version of the iPhone’s built-in app, but I’m a fan because of the way it syncs to outside services like Dropbox. Getting data to the next place you’re going to consume it is the key,” says Phillip Leslie, CEO of ProOnGo LLC.

SOMETHING ELSE TO TRY: “Really advanced mobile workers like (Mr. Ettinger) have figured out how to complete 90% of their tasks using mobile devices, and they’re trying to tackle that last 10% where you’re still chained to your desk,” Mr. Leslie says. “They’re using GoToMyPC to access their office computers from a mobile device to complete those tasks.”

Sandy Marshall's firm, Marshall Creative, specializes in short films, audio projects and other digital content that's often too large to email. He uses the cloud-storage app Jungle Disk to solve that problem.

When Sandy Marshall is out of his office, the CEO of Chicago marketing firm Marshall Creative is as likely to be on a Caribbean cruise as at a client meeting across town. That’s because Mr. Marshall has a second job as a director for Second City’s comedic performances aboard the Norwegian Spirit, a cruise ship operated by Norwegian Cruise Lines.

The challenge for Mr. Marshall isn’t just staying in touch, it’s that his firm specializes in short films, audio projects and other digital content that’s often too large to email. He uses the cloud-storage app Jungle Disk to solve that problem. Through Jungle Disk’s free app (which requires a paid subscription to the storage service offered by Suwanee, Georgia-based Jungle Disk LLC ), Mr. Marshall has access to the 100 gigabytes of content that Marshall Creative stores online, even when he is at sea.

Mr. Marshall uses a similar free app, Dropbox, for client meetings and to share large files with clients. San Francisco-based Dropbox Inc. offers its users 2 GB of free cloud storage, and Marshall Creative uses a free account to host individual files for presentations.

“I’m always a fan of in-person presentations, and getting that response,” he says. “With Dropbox, it’s a little easier (than with JungleDisk) to access audio and video files during a meeting.”

WHY IT WORKS: “Dropbox is far and away the best application, mobile or otherwise, to share multimedia files among co-workers. It works great on the iPhone, iPad and Android devices,” says Brad Spirrison, managing editor of the Chicago app-review company Appolicious Inc.

SOMETHING ELSE TO TRY: “Later this year Apple will be coming out with its own document-sharing service, which could be superior to Dropbox, at least on Apple products,” Mr. Spirrison says. “However, it is unclear if or how that product will interface with users with Android phones or BlackBerries.”

Helmut Jahn has largely ignored the personal computer. The architect considers the device too complicated, too big and too heavy compared to his creative tools of choice: a sketchbook and camera. For years, as he traveled around the world, Mr. Jahn used fax machines to send and receive drawings to and from his firm’s Chicago headquarters.

Then, about eight months ago, his friend Howard Ecker introduced him to Apple Inc.’s iPad, and the device spurred a technological revolution in Mr. Jahn’s life.

“It has transformed how I think and how people in my office communicate with me,” Mr. Jahn says. First, he’s a more active emailer and better prepared for client presentations. But the centerpiece of his iPad usage is the $4.99 app SketchBook Pro, a drawing program from Autodesk Inc., the San Rafael, Calif.-based software company that also makes the AutoCAD engineering and architecture software.

Mr. Jahn, 76, estimates that he now uses SketchBook Pro for 90% of the drawings he makes while on the road, and even uses the program about a third of the time while working in his Chicago office. He also takes photographs of his sketches, then imports those images into SketchBook Pro so he can make notes and export the images. Drawings from SketchBook Pro can be emailed or transmitted to cloud-storage programs such as Dropbox.

Learning to draw on the iPad required an adjustment, but not a severe one.

“It’s a different medium, but the adjustment was no more different than working with a different pen or different paper,” says Mr. Jahn, who uses a stylus with SketchBook Pro. His drawings using the app “look a little more sketchy (than a similar drawing on paper), but I can actually work faster because I’m not attempting to get that accuracy.”

From processing credit cards to sketching skyscrapers, an increasing number of small businesses are harnessing the power of their smartphones and iPads.

Justin Seidenberg needs to be able to talk to his artists even when he's out of the office. Photo by: Erik Unger

Justin Seidenberg is accustomed to crises erupting at odd hours. Mr. Seidenberg manages a stable of musicians through his Chicago company, Kiqstart Music LLC, and it’s when his artists are at performance venues that they are most likely to require his help. In other words, he needs to be ready for action at 11 p.m. on a Saturday night.

“I’m out having dinner with my wife, but my artist gets to the venue and gets into a debate with the production manager. I need be available and prepared,” he says.

Mr. Seidenberg uses two iPhone apps to meet the challenge. The first is Skype, a free app from Palo Alto, Calif.-based Skype Inc. that allows him to video chat with his musicians, wherever they may be.

The second is GoogDocs from Fossil Software LLC of Austin, Texas. This app allows Mr. Seidenberg’s mobile phone to access spreadsheets he creates using Google Docs, Google Inc.’s free, cloud-based office suite. He keeps contract details there, such as the set length, sound-check time and financial arrangements between artist and venue, so he can quickly intervene if a dispute arises.

WHY IT WORKS: “A (video chat) app like Skype provides an extra layer of interaction that helps reinforce your message. If you have to air a grievance or a concern, a visual rendering can carry a lot more weight,” says Chris Pautsch, CEO of KeyLimeTie LLC.

SOMETHING ELSE TO TRY: For more formal video conferencing, Cisco Systems Inc. offers a free mobile app for users to join meetings that use the company’s WebEx Meeting Center. Mr. Pautsch uses the service at KeyLimeTie to stream video and share documents among participants.

There’s a common line among social-media critics that goes something like, “No one wants to hear what you ate for lunch today.” But that might depend on who you are and what you had for lunch.

Chicago restaurateur Billy Dec, for example, took a picture of the goulash he ordered during a recent trip to Budapest, and 45 minutes after he posted the photo on Twitter, 608 people had clicked the link to see his bowl. Mr. Dec, who owns four entertainment venues, including River North eateries Rockit and Sunda, commands a legion of more than 17,000 Twitter followers. His goal is to share his behind-the-curtain access to such scenes as a popular chef at work in the kitchen and a celebrity musician backstage.

He uses the free mobile-phone app UberSocial from Pasadena, Calif.-based software firm UberMedia Inc. Mr. Dec has been using the app for about six months and says its immediacy “allows you to see magic behind Twitter because everything is just instantaneous.”

Mr. Dec aims for 10 to 12 tweets per day.

“I feel bad if it’s more than 10 a day, but I also feel bad if I don’t get close to that because people have expressed an interest,” he says. “I didn’t realize people cared as much about this behind-the-scenes stuff as they do.”

WHY IT WORKS: “UberSocial has some neat features. It’s great to click on a tweet that includes a link and be able to see the web page in the same window,” says Brad Spirrison of Appolicious Inc. “UberSocial’s ‘Channels’ are a handy way to access ‘conference’ or ‘breaking news’ tweets.”

SOMETHING ELSE TO TRY: “Seesmic is a similar tool that allows you to view and update accounts for Twitter, Facebook and even multiple blog posts. It’s also easier to switch between multiple Twitter accounts (than with UberSocial). The free app lets you add Twitter accounts as giant buttons, so it’s easy to use in a dark nightclub,” Mr. Spirrison says.

Should you trust an app from an unknown developer?

Solo and small-shop app makers “are often creating the most innovative apps available,” according to Brad Spirrison, managing editor of the Chicago-based app-review company Appolicious Inc. However, it’s wise to vet any app before you start using it. To do that, Mr. Spirrison recommends reading reviews in Apple’s App Store and Google’s Android Market, as well as on Facebook, in industry publications and on sites such as Appolicious.

It’s also worthwhile, even if you don’t have an iPhone or iPad, to see if Apple has approved an app.

“There is a higher bar set for getting an app approved for use on Apple’s iOS devices than by Google for use on its Android devices,” Mr. Spirrison says. “If an app is approved or promoted by Apple, that’s a good sign.”